The interior angle of a regular octagon is 135 degrees.
An octagon is a polygon that has 8 sides. Therefore, a regular octagon is a octagon with all it sides and angles equal to each other.
Therefore, the sum of angles in an octagon is each interior angle multiply by the number of sides.
Therefore,
n = number of sides = 8
Hence,
interior angle = (n - 2)180 / n
interior angle = (8 - 2)180 / 8
interior angle = 6 × 180 / 8
interior angle = 1080 / 8 = 135°
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